1. Field of the Invention
The present invention relates to an optical cable, and more particularly to an optical cable having an improved compression strength characteristic as compared to conventional optical cables.
2. Description of the Related Art
Conventional optical cables may be classified according to the installation method of the optical cable. For example, duct line optical cables are installed in ducts that have been buried in the ground; buried optical cables are directly buried in the ground; and aerial optical cables are installed in the air using poles.
FIG. 1 shows a typical buried optical cable. The optical cable 100 includes a central tension member 110, a plurality of tubes 140, a binder 150, a first sheath 160, a tension member 170, and a second sheath 180.
The central tension member 110 is positioned in the center of the optical cable 100. It may be a rod type member having a circular sectional shape. It provides the optical cable 100 with tensile strength.
The tubes 140 are positioned around the central tension member 110. They are oriented parallel to the central tension member 110 and have a hole in the center thereof. A plurality of optical fibers 120 is positioned in the hole of the tubes 140. The space within the tubes 140 is filled with jelly 130. The jelly 130 absorbs moisture that has penetrated into the tubes 140.
The binder 150 is positioned around the plurality of tubes 140. It is of a tape type and surrounds the tubes 140 to hold them.
The first sheath 160 is positioned around the tubes by an extrusion process.
The tension member 170 is positioned around the first sheath 160. It may be helically wound around the first sheath 160. The tension member 170 provides the optical cable 100 with tensile strength and may include a number of aramid yarns.
The second sheath 180 is positioned around the tension member 170 by an extrusion process.
Use of such a typical buried optical cable 100 requires that a trench be dug in the ground for installation, which is a costly procedure considering both time and money. In the case of using a duct line optical cable, the ground must also be dug before installing conduct lines.
The conduct line optical cable and the buried optical cable have low compression strength and cannot be installed on the ground while being directly exposed to external environment.
Accordingly, there is a need in the art for an optical cable that has improved compression strength and can be installed on the ground, e.g., on the ballasts near railroads. Such an optical cable must be able to withstand a certain loads, e.g., a load from a track vehicle for railroad maintenance.